This invention relates to an improvement in the known process for preparing methylchloroform (1,1,1-trichloroethane), a commonly used degreasing solvent, by reacting chlorine and 1,1-dichloroethane in the vapor phase. In addition to methylchloroform, the vapor phase chlorination produces hydrogen chloride, vinylidene chloride, vinyl chloride, unreacted 1,1-dichloroethane, 1,1,2-trichloroethane, 1,2-dichloroethylenes and other higher chlorinated hydrocarbons. Both vinyl chloride and vinylidene chloride may be separated from the reaction mixture and catalytically hydrochlorinated, utilizing the liberated hydrogen chloride, to 1,1-dichloroethane and methylchloroform respectively. The 1,1-dichloroethane may be recycled to the chlorination feedstock and the methylchloroform may, of course, be combined with the methylchloroform separated from the original reaction mixture.
Since the remaining reaction products, i.e., 1,1,2-trichloroethane, 1,2-dichloroethylenes and higher chlorinated hydrocarbons, are not readily and economically separated or converted to useful products, it is desirable to suppress the formation of these undesirable reaction products. In a typical vapor phase chlorination of 1,1-dichloroethane, it has been found that about 30 or more pounds of these undesirable chlorohydrocarbon reaction products are produced per 100 pounds of methylchloroform product.
Methylchloroform product as used herein refers to the methylchloroform produced directly by the vapor phase chlorination of 1,1-dichloroethane as well as methylchloroform that would be produced were the vinylidene chloride produced by the vapor phase chlorination of 1,1-dichloroethane catalytically hydrochlorinated to methylchloroform.
In copending, commonly assigned U.S. application Ser. No. 879,029, filed Feb. 21, 1978, it is disclosed that the formation of undesirable chlorohydrocarbon reaction products may be suppressed by conducting the vapor chlorination of 1,1-dichloroethane in the presence of a controlled amount of elemental oxygen.